Fix rollout_id warning for default LM temperature (#9316)

Author: okhat

dspy/clients/lm.py

@@ -111,7 +111,7 @@ def __init__(
         self._warn_zero_temp_rollout(self.kwargs.get("temperature"), self.kwargs.get("rollout_id"))
 
     def _warn_zero_temp_rollout(self, temperature: float | None, rollout_id):
-        if not self._warned_zero_temp_rollout and rollout_id is not None and (temperature is None or temperature == 0):
+        if not self._warned_zero_temp_rollout and rollout_id is not None and temperature == 0:
             warnings.warn(
                 "rollout_id has no effect when temperature=0; set temperature>0 to bypass the cache.",
                 stacklevel=3,

tests/clients/test_lm.py

@@ -190,7 +190,7 @@ def fake_completion(*, cache, num_retries, retry_strategy, **request):
 
     monkeypatch.setattr(litellm, "completion", fake_completion)
 
-    lm = dspy.LM(model="openai/dspy-test-model", model_type="chat")
+    lm = dspy.LM(model="openai/dspy-test-model", model_type="chat", temperature=0)
     with pytest.warns(UserWarning, match="rollout_id has no effect"):
         lm("Query", rollout_id=1)
     with warnings.catch_warnings(record=True) as record:
@@ -199,6 +199,23 @@ def fake_completion(*, cache, num_retries, retry_strategy, **request):
         assert len(record) == 0
 
 
+def test_rollout_id_with_default_temperature_does_not_warn(monkeypatch):
+    def fake_completion(*, cache, num_retries, retry_strategy, **request):
+        return ModelResponse(
+            choices=[Choices(message=Message(role="assistant", content="Hi!"))],
+            usage={"prompt_tokens": 1, "completion_tokens": 1, "total_tokens": 2},
+            model="openai/gpt-5-nano",
+        )
+
+    monkeypatch.setattr(litellm, "completion", fake_completion)
+
+    with warnings.catch_warnings(record=True) as record:
+        warnings.simplefilter("always")
+        lm = dspy.LM(model="openai/gpt-5-nano", model_type="chat", rollout_id=1)
+        lm("Query")
+        assert len(record) == 0
+
+
 def test_text_lms_can_be_queried(litellm_test_server):
     api_base, _ = litellm_test_server
     expected_response = ["Hi!"]